The present invention relates to refrigeration systems, and more particularly to an apparatus and method for purging non-condensable gases from a refrigeration system.
In a conventional refrigeration system, particularly in low pressure centrifugal compressor systems, the leakage of air, water vapor, and other contaminating foreign gases into the system is a recognized problem. Such gases reduce the efficiency of the system since they tend to elevate the total pressure in the condenser, and thus more power is required from the compressor per unit of refrigeration. Also, these foreign gases tend to cling to the condenser tubes thereby reducing the total condensing surface area.
To remove these foreign gases from the system, it is common practice to draw a mixture of the gaseous refrigerant and foreign gases from the high pressure region in the condenser or receiver where they normally accumulate, condense the refrigerant and any water vapor by cooling or by compression and cooling, vent off the non-condensables, separate and drain the water, and return the condensed refrigerant to the low pressure region of the system. Typically a purge apparatus is used to remove foreign gases from the refrigeration system in the above manner. A conventional purge apparatus typically comprises a purge chamber wherein the non-condensables gather above the liquid refrigerant and water. A pressure actuated mechanical relief valve automatically opens to vent the non-condensables to the atmosphere through a gas discharge line, and a manual drain is provided to drain off the water which floats on top of the liquid refrigerant. A mechanical valve adjacent the bottom of the purge chamber is opened by a float to drain the condensed refrigerant through a refrigerant line and return it to the low pressure region of the system.
U.S. Pat. No. 3,664,147 to Blackmon discloses an improved purge apparatus that is similar to but improved beyond the type described above. The improved purge apparatus includes an electric float switch in the purge chamber and which is connected to a pair of solenoid actuated valves for (1) discharging a portion of the condensed refrigerant through the refrigerant line to the low pressure region of the refrigeration system when the level of condensed refrigerant rises above a predetermined level, and (2) venting the non-condensable gases to the atmosphere through the gas discharge line when the level of the condensed refrigerant drops below a predetermined level. The apparatus described in the referenced patent has been commercialized in a configuration wherein a compressor is provided in the gas discharge line to facilitate withdrawal of the gas from the purge chamber, which is particularly useful when low operating pressures are utilized in the refrigeration system.
While conventional purge apparatuses such as, but not limited to, those described above are efficient, it is recognized that non-condensed refrigerant remains with the contaminating non-condensable gases in the purge chamber and is vented to the atmosphere through the gas discharge line during the purging operation. Thus, more modern purge apparatuses include many refinements and, as a result, are more efficient (i.e., vent less non-condensed refrigerant to the atmosphere) than the conventional purge apparatuses discussed above. Also, apparatuses that supplement purge apparatus have been developed which also seek to minimize the venting of non-condensed refrigerant from purge apparatuses to the atmosphere.
Examples of more modern purge apparatuses are disclosed in U.S. Pat. Nos. 5,261,246 and 5,313,805, issued to Blackmon et al. These patents disclose the employment of a gas separation tank that is in fluid communication with the gas discharge line. Refrigerant is further separated from non-condensable gases in the gas separation tank. Among many other improvements, these two patents further disclose, in certain embodiments, the placement of refrigerant adsorbing material within the gas separation tank, whereby the adsorbent material adsorbs non-condensed refrigerant passing through the gas discharge line. The adsorbed refrigerant is cyclically withdrawn from the adsorbent material and routed back to the refrigeration system by way of tubing that is part of the purge apparatus. In one configuration the gas separation tank is periodically placed solely in fluid communication with the evaporator such that adsorbed refrigerant is drawn from the adsorbent material to the evaporator. Also, the gas separation tank is heated, which heating tends to drive the adsorbed refrigerant from the adsorbent material. These and other of the more modern purge apparatuses are typically integrated purge apparatuses which are sold as complete units. Accordingly, if it is desirable to decrease the amount of refrigerant that is allowed to vent from a refrigeration system equipped with a less modern purge apparatus, the less modern purge apparatus is often totally replaced with one of the more modern purge apparatuses.
However, it is recognized that even more modern purge apparatuses vent some refrigerant to the atmosphere. It is also recognized that it is sometimes not desirable to completely replace a less modern purge apparatus. Accordingly, a purge supplement apparatus has been developed. The purge supplement apparatus is interposed between the purge apparatus and the atmosphere. That which is vented from the purge apparatus passes through the purge supplement before being released to the atmosphere. The known purge supplement consists of two vessels that are arranged in series and which contain a refrigerant adsorbing material therein. As the purge apparatus vents to the purge supplement, non-condensable gases tend to pass through the purge supplement while refrigerant tends to be adsorbed by the adsorbent material in the purge supplement. It is conventional for the purge supplement to periodically be totally separated from the purge apparatus and be transported to a facility where the adsorbed refrigerant is extracted from the purge supplement. The purge supplement is then reinstalled to the purge apparatus for further use, and the refrigerant extracted from the purge supplement can be manually added to the associated refrigeration system for further use. While the conventional purge supplement seeks to lessen the venting of refrigerant to the atmosphere, it is considered by some to be cumbersome with respect to the that that human labor is required to maintain the operation of the purge supplement.